Earlier quoted context omitted.
As a frontend dev there are definitely well designed frontends. I've seen a lot of bad backends too. It just depends on how much engineers are able to plan ahead and also keep tech debt under control.
I would say it's not so much about good or bad design, and more about which kinds of decisions, how many moving parts, and what consequences they have down the line. Like on backend you will have a choice of database, choice of language, and the design of the Schema/API, most of which are easy to detach and replace at some point. While on Frontend from the beginning, specially i you are working with a team, you will…
I have yet to work on a React + Tailwind codebase in the wild where the margin/padding metrics aren't hardcoded and repeated across tens of different components. We've traded the elegance of well-written SCSS for improved developer ergonomics and faster build times because webpack is so slow at compiling stylesheet changes.
If you want to practise proper DRY for spacing, typography, etc. in a React app, you'll just end up nesting tons of components that ultimately result in needless complexity.